Filters employing tubular filter elements into and through which the liquid is to be filtered is pumped have been successfully used for many years. Such filter elements have employed rigid perforate support tubes enclosing a finely perforated inner sleeve in which the solids entrained in the filtrate are collected. Such external support tubes have generally been formed of metal. However, because many liquids to be filtered react with most metals, for many applications the support tubes cannot economically be formed of metal. Attempts to replace the conventional metal support tubes with plastic tubes have not been successful because presently available plastics do not have the required strength to withstand the forces exerted on such tubes during normal operation of the associated filters. Consequently, other types of filters which are inherently less efficient for particular applications have nevertheless been used where the cost and size of the support tubes is prohibitive.
In the past it has been both difficult and time consuming to clean those types of filter tubes in which the solids are internally collected, and the problem is more acute where the collected solids are toxic in nature.